Electric horns for vehicles currently in use comprise, in general, a linear electromagnetic motor mechanically coupled with a sound generating diaphragm which is acoustically coupled with the air column of a sound projector. The motor is mounted within a housing and the diaphragm is mounted on the housing with its periphery in sealing engagement therewith to provide a chamber containing the motor. The motor comprises an annular field coil within a cup-shaped portion of the housing and a pole piece is mounted coaxially of the coil on the bottom wall of the cup-shaped portion of the housing and extending therethrough. A plunger or armature is disposed coaxially of the coil and is mounted on the diaphragm for reciprocating motion along the axis of the coil with an axial air gap between the armature and the pole piece. Thus, a magnetic circuit or flux path is provided through the pole piece, housing, diaphragm, armature and the air gap. The motor is adapted to be energized from the vehicle battery through switching contacts which are opened and closed by the motion of the plunger which vibrates the diaphragm to generate sound energy. In order to obtain the desired level of sound output, the air gap must be adjusted to a predetermined dimension. This adjustment of the air gap is achieved by deforming the bottom wall of the cup-shaped housing to properly locate the pole piece and adjusting cap.
It is desired to improve the operating efficiency and the stability of electric horns of the prior art. The Neese U.S. Pat. No. 4,361,952 granted Dec. 7, 1982, is typical of such prior art. The horn described in the Neese patent has a pole piece with a reduced diameter portion which is press fitted into an opening in the bottom of the cup-shaped housing. A threaded stud on the pole piece serves as a mounting member and an electrical ground connection for the horn. The air gap between the pole piece and the armature is adjusted after assembly by deforming the bottom wall of the cup-shaped housing. The deforming force is applied to the stud on the pole piece and the sheet metal wall of the housing is bent in the vicinity of the pole piece, commonly referred to as the pole piece and adjusting cap and hereinafter referred to as the pole piece/adjusting cap. While the horn of this type has been satisfactory, it is desired to provide improved magnetic circuit efficiency and stability of the pole piece/adjusting cap in its relationship with the armature.
A general object of this invention is to provide an improved pole piece/adjusting cap for an electric horn to overcome certain disadvantages of the prior art.